1. Jamie A. Johansen 1, S. Marc Breedlove 1,2, Cynthia L. Jordan 1,2 1 Neuroscience Program, 2 Department of Psychology, Michigan State University johanse8@msu.edu Flutamide Rescues Transgenic Male Mice from the Toxic Effects of Over-expressing Wildtype Androgen Receptors in Skeletal Muscle Fibers Introduction Methods Spinal Bulbar Muscular Atrophy (SBMA) is a heritable X-linked, slowly progressive lower motor neuron disease characterized by adult onset of muscle weakness, atrophy, and loss of motoneurons. We created a transgenic mouse line in which a rat AR cDNA with a wildtype (Wt) number of glutamine residues (22) is over- expressed in muscle fibers using an HSA (human skeletal actin) promoter. Unexpectedly, tg male mice as adults show a disease phenotype typical of SBMA in humans. Very few transgenic males survive to weaning and recent evidence suggests that many tg males die on the day of birth. Given that tg females do not experience a similar mortality, we suspect that perinatal testosterone may cause many tg males to die as newborns. To examine whether blocking androgen action prenatally would protect our tg males from death on postnatal day 1, we treated pregnant dams with 5 mg flutamide/day on gestational days 15-20. Construct: AR cDNA was subcloned from pCMVAR. cDNAs were ligated into the NotI site of pBSX-HSA. Prenatal Flutamide: 5 mg flutamide/day on gestational days 15- 20 was given to pregnant dams. Behavioral Testing: Hang Test - Mice were placed on a wire grid, and then turned upside down, and the time to fall was measured in seconds. Paw Print Analysis – Front feet were painted with non-toxic acrylic red paint, and hind feet were painted with blue. Mice were then guided to walk along a strip of filter paper. Histology: Extensor Digitorum Longus (EDL) muscles were dissected from transgenic and wildtype males, cryostat sectioned at 10um, and stained for hematoxylin and eosin (H&E). Ventral roots were embedded in plastic and 1µm cross-sections were stained with toluidine blue. Prenatal flutamide treatment was successful in rescuing transgenic (tg) males from death. Tg males and their wildtype brothers were feminized, showing shorter ano-genital differences than untreated males. Tg males weighed less, and developed signs of SBMA as they reached adulthood. This included kyphosis, and a profound loss in muscle strength indicated by the hang test. Loss of muscle strength is an early indicator of the disease. However, stride length was not decreased suggesting that the disease in flutamide treated males had not progressed to late- stage SBMA. Tg males showed a reduction in the number of EDL muscle fibers, but no change in average fiber size. Tg males did not show a reduction in the number of L5 ventral root axons, also suggesting that the disease has not progressed to late-stage SBMA where motoneurons begin to die. No change in average axon size was seen. Technical support was provided by Cindy Knaff, Chas Jensen, and Sandy Troxell. These studies were funded by NIH NS-045195 (CLJ) and the MSU foundation (CLJ). This work demonstrates that prenatal flutamide can rescue tg males from death on postnatal day 1 but is not sufficient to prevent the eventual emergence of SBMA later in life. Flutamide treatment may delay the onset of SBMA, and disease progression may be slower in flutamide treated males. These results suggest that the wildtype AR, at sufficiently high levels, is toxic to muscle fibers. Ultimately, loss in muscle fiber function may lead to a loss of fibers, and eventually to a loss in motor neurons. Our results also suggest that SBMA and other motor neuron diseases may be myogenic in origin, contrary to the prevailing view. Summary Significance Acknowledgments